NASATechnical Paper 3150FeasibilityStudy ofaLow-Energy Gamma RaySystem forMeasuringQuantity and FlowRateof SlushHydrogenJag J.Singh,Chih-PingShen, andDanny R.SprinkleApril 1992

Ab stractAs part ofastudy todemonstratethe suitabil-it y of anX-rayorgammaray probe formonitoringthe quantity and flowrateofslushhydrogen, massat tenuationcoefficientsforCd109X-andgammara-diationin ve chemic al compoundshavebeen mea-sured .TheAg109KXrayswere usedfor waterandaceticacid, whereasE3 transitionfrom th e rstex-citedstate at87.7keVinAg109providedtheproberadiationfor bromobenzene,ff2-chloroisodurene, andcetylbromide.Measurements weremadeforasinglephase (gas,liquid,andsoli d)aswellasmixedphases(liquidplus solid)in allcases. It has beenshownthatt he massattenuationcoeffici entfor theselectedra diationsisindependent of thephaseofthetestflu-idsorphaseratiosinthe case ofmixed-phase uids.Th isreport describes the procedureandresults forthefive uidsystemsinvestigated.Introductio nSlu sh hydrogen isbeing considered(refs.1 and 2)as apropellantforthe NationalAero-SpacePlane(NASP).Ithaslow mass, highenergycontent,andhigherdensitythanliquid hydrogen.However,nosuitable techniquei scurrentlyavailable formonitor-in gthequantityandflowrateofafuelwhosephaseconfigurationiscontinuouslychanging.We havein-vestigated thefeasibilityofalow-energygammaraysystemforgaugingthe quantityandflowrate forsuch fuels. Itisbased onthe principlethatthe massat tenuationcoefficient ofachemicalcompoundforgammaradiationdoes not dependon the phaseofthech emical.Thisreportdescribes theresults forfivemixe d-phase uidsystems.TheoreticalBackgroundWhen anarrow beam of gammarays passesthro ugh matter, someof th erays are scattered orabsor bedinthemediumbecauseof interactionswiththe atoms of the medium.Forexample,I=Ioe??x(1)whereIintensityofgamma radi ationarriving atde tectorIointensityofgamma radi ationincidentontestmedium?attenuationperunitpath length in themedi um(i.e.,the linear attenuationcoefficient)xpathlengthin themediumThel inearattenuation co efficient(?, cm?1) foraneleme ntalmediumisgivenby?=oen=oeNaeA(2)whereoetotalinteraction crosssectionperatom,c m2/atomNAvogadro'snumberonphysicalscale,6:025?1023atoms/moleaedensity of themedium, g/cm3Aatomi cor molecularweight, gS inceoeisafunctionof gamma rayenergy,?isclearlyenergy dependent. Theexpression for? c anbegen eralizedforany medium containing diff erentkindsofatoms. It isthe basisof theconventionalnuclearradiationattenuation(NRA)monitors.Amoreuseful variationofequation(2)is?ae=oeNA(3)where?=aeisinunitsof centimeterssquaredpergramandcalledthemass attenuationcoefficientofthemediumforthe incident gammarays. Mass atten-u ationc oefficient isamorefundamental parameterthanthelinearattenuationcoefficientsince it is in-d ependentofthe actual densityandphysical stateofthe medium.Ifthemediumisamixture ofseverald ifferentcompound sor elements,its massattenua-tioncoe fficient isgivenby??ae?mixture=Xiwi??ae?i(4)wherewifraction byweightoftheithcomponent??ae?imassattenuation coefficient of thei thcomponentForamultiphase mixture ofanygivenchemicalcompound ,equation(4)can bewritten asfollows:1

??ae?multiphase=3Xi=1wi??ae?i=w1??ae?solid+w2??ae?li quid+w3??ae?gas=??ae?single phase(w1+w2+w3)=??ae?single phase(5)Itis thereforeexpectedthatameasurement of linearat tenuationcoefficient?mixtureforamultiphasemix-tureofagi vencomp oundshouldprovide its instanta-ne ous densityaemixture, since?=aeforanyofits singlephasesispresumablyalread yknown. Exploitationofthis principleinthe NASPprogramwillrequiresi-multaneousmeasure mentoffuel volumeby judiciousloc ationsofseveralcountingsystemsinthefueltank(ref.3). If total fuel volumemeasu rementsare madeevery second,therateofdecreaseoftheremainingfuelinthe tankshouldequ al its rate of consumption(o r flow rate outofthefueltank).ExperimentalProcedureandResultsFivemultiphasesystems wereselected toverifytheprincipleofphase mixtures.Theywerewa-ter, acetic acid,bromobenzene,ff2-chloroisod urene,andc etyl bromide. These syste mswere selectedfo rconvenience of handlingandappropriaten essoftheir physicalproperties,assummarized in tableI.T able I. SummaryofChemicals StudiedMe ltingBoilingChemicalChemicalpoint,point,purity,percentspecie sffiCffiC(a)Water0.0100.0100Aceticacid16.6118.599.9ff2-chloroisodurene33.4122.598Bromobenzene?31.0156.099Cetylbromide18.0149.097aExceptforacetic acid, allchemicalswere obtainedfromAldric hChemicalCompany. Aceticacid wassuppliedbyJ.T.BakerChemicalCompany.Allsystems exist in liquidphaseatroomtemperature(25ffiC)exceptff2-chloroisod urene. They can beso-lid i edandvaporizedrathereasily. TheCd1 9/Ag109radionuclide was selectedas th esource of probingph otons. It has a reason able half-life(454 days)an demits appropriate energy photons. TheX-an dgammaradiationphotonswere countedwith aNaI( Tl) counter. Theattenuationcoefficientmea-surements weremade in standard narrow-beam ge-omet ry(ref.4). Allmeasurements weremade at thetempe raturesnecessaryfor theappropriatephases ofthe testchemicals.For instance, in thecaseofwater,?gaswas measuredat100ffiC,?liquidwas measuredatroom temperature(25ffiC), and?solidwas measuredat0ffiC.Figure 1showsthe schematicdiagram of theex perimental system.The testcel lfor liquid, solid ,an dliquid plus solid mixtures of phases ofwaterandaceticacidcon sistedofamulticomponent51- by51-by 51-mmDupont Teflon cube, shown in gure2.T heother threechemicals weretested in a special lyd esignedquartzcell,shownin figures 3 and 4. Anap propriatelyheated 102-mm-long quartz cylindri-calce ll,throughwhichvap orsfrom theboiling liq-u idswerepassed, wasused top rovide aselected gasmed ium forX-rayattenuationmeasurements. (Seeg. 5.)Th egas-phase densitieswere calculatedfromtheidealgaslaw (i.e.,aegas=PM=RT, w herePisthepressure,Risthe gasconstant,Tisthe va-portemperature, andMi sthe molecularweightofthechemi calcompound).Theliquid-phase densitiesweremeasuredwitha precision specificgravitychainbalance,accurateto0.0001. Thesolid-ph aseden-sityvaluesweredeterminedby extendingthegraphofaeliquidversusTfor thetestchemicaltoa temper-ature 5ffibelowitssolidification temperature.1Theslushdensities,on theotherhand, weredeterminedfromthegraph ofaeli quidversusTexactlyatthe melt-ingpointofthe solidphaseofthechemical. Theli quid-phaseden sitiesweremeasuredat aminimumofsixtemp eraturesfor agood le ast-squareslinearfittothe data foraeliquidversusT.Theresults are summarizedin table II andil lustrate d in gure6. Thelast columnintable II(c) lists the theoretical valu e of massat-tenu ationcoefficientof thespecies tested (ref. 5).It should be noted that we have included twootherch emi calcompounds (nitrogenan d dibro-mom e thane) in tableII and gure 6, eventhoughthey requiredhigherenergy gamma rays formeasur-in gtheir?=aevalues. It is apparent fromthedata1Inthecaseof water,ice den sityaesoli dwas takenfrom theHandbook of ChemistryandPhysicsandtheslushdensityaeslushwas calculatedfor severa lpercentagesof iceinwater as follows:aeslush=M1+M2(M1=ae1) + (M2=ae2)whereMiandaeiare themass anddensity of thei thphase(iceorwater).2

thatthe valuesofthemassattenuation coefficientsfor allthesystems areindependentoftheir physicalst ates.Asafurthertestof th evalidityofequation (5),the experimental and calculatedvaluesofthedensi-tiesofmultiphase mixturesofff2-chloroisodureneandaceticacidwerecompared.Theexp erimentalvaluesofthe densityof themixtureaee xpweredeterminedfrom?exp=(?=ae)theoryrati os forthetestchemicals.Thecalculated valu es ofthe densityaec alweredeter-minedfromthefollowin grelation:aecal=l1ae1+l2ae2+l3ae3l1+l2+l3whereliandaeirepresentthepathlengthanddensityofthe individualphases (solid,liquid,an dgas)of thetes tchemicals.Theresults forff2-chloroisodurene areaeexp=1:0331?0:0124 g/cm3andaecal=1.0392 g/cm3.For acetic acid, the resu ltsareaeexp=1:0619?0:0127g/cm3andaec al=1.0590g/cm3.Discussio nof the Propo sedSlushH ydrogenMonitori ngSystemFigure7showsaschematic diagram of the pro-p osed slush hydrogenmonitoringsystem.It is as-sumed that the interface ofgaseous hydrogenandslu sh hydrogen w ill remaina well-define dplanewith-outtheuseofanappropriate re straining diaphragm.2Itis alsoassumedthattheslush hydrogenmixtureiswel lstirredto ensure itssteadyo wandtoavoidsedimentationof solidhydrogen.3For clarityonly a single pairof de tectors areshown . Obviously,several suchpairs will beneededto determinethevolume ofthefuelin the tanks(r ef.3).Thehorizontaldetectorsystem in figure 4 canp rovide th eslu sh densityaeslushasshownbelow. LetI (d2)bethecou ntingrateatdetector2:I(d2) =Ioe??slushd2(6)where2Operation inmicrogravity environmentmightdictate thene cessityfor arestrainingdiaphragm.3Activesteps willhave tobetakentoensurethevalidityofthese assumptionsifslushhydrogen is to beusedasapropellantfor NASP.4

d2distancebetween thesource andthedetec-t or in horizontal systemI oincide ntphotonfluxinthehorizontalsystem?slushlinear attenu ationcoefficientforslushhydro genin thehorizontalpathWith?slush=aeslush=?liquid=aeliqu idknownfrom sys-temcalibrationdata,equation (6 )caneasily provid eae slushfromameasurementof?slush.Thehydrogenslushlevelatanytime|andh encethe totalslushvolume in the tank|can bedeter-mine dwiththe verticaldetectorsystem. Suppose thein stantaneousheightof the gaseoushydrogen{slushhydrogeninterfaceisx. Thenthecou ntingrateI(x)atdetector1isgivenby the followingexpression:I(x) =I0oexp???slushx??gas(d1?x)?(7)whereI0oincidentphotonfluxinthevertical system(itc an bearran gedto beequ al toI o)d1distancebetween thesource and th ede-tecto rinthe verticalsystem (itcan b ear-ranged to equald2)?gaslinear atte nuationcoefficientingaseoushydrogenTheonlyunkn own in equation(7) isx , since?slushisalreadyknown fromequation(6) and?gasi seasilycalculablefromthefollowingequation:?gasaegas=?liqu idaeliquid=?ae(8)where?=aeisthe calibration constantfor hydrogen.Asimultaneousmeasurementoftemperatureandpressureofthe pressurizinghydrogengascan providea valueofaegasandthusenableacalculationof?gas.Since linear attenuationcoefficients are strongfunc tion softhephoton energy and thetestmedi umat omicnumber,itwillben ecessarytousemuch loweren ergygamma ray sourcesfor slushhydrogen mea-surem ents.A5.9-keV Fe55/ Mn55sourceshouldservethe purposewell, asindicatedby typical calculationsfor slushhydrogen(50percent solid):I (x) =Ioe??x=0:52Io(x=25cm)=0:26Io(x=50cm)Clearlythereisa reasonably strong attenuation,con-comitan twithastatistical ly strong survivalrate, forthe 5.9keVXraysthroughappropriate path lengthsin slush hydrogen.Anadditional advantageof usinga low-energyradiationsource is the convenienceofshi eldingagain st it.C oncludingRemarksMass attenuation coefficientsfor Cd1 9radiationhavebeen measuredinanumber ofmixed-phase u-id s.Thesemeasurements have clearlyconfirmed,asexpected, th at the massattenuation co efficients forX andgamma raysinflui ds are independ entof thep hysicalphasesofthefluids.Itcan thereforeb econ-cludedthatasimilarsystembasedon anappropriatephotonsource|suchas Fe55/Mn55(5.9keV)|canserveasthebasis forslush hydrogen monitoringon-boardtheNationalAero-SpacePlane.NASALangleyResearchCenterHampton, VA23665-5225February20, 1992References1. Ludtke,PaulR.;and Storch,PeterJ.:Surveyof Instru-mentation forSlushHydrogenSystems.NASPTM-1054,NASPJointProgram O ffice,Wright-PattersonAirForceBase, 1989.2.Kandebo, StanleyW.:ResearchersEx ploreSlush Hy-d rogenasFuel forNationalAe ro-Space Plane.AviationWeek & Space Technol.,vol. 130,no. 26,June26,1989,pp.37{38.3.Singh,Jag J.;Mall, GeraldH.; Sprinkle,DannyR.;andChegini,Hoshang:FeasibilityofaNuclear GaugeforFuelQuantityMeasurementAboard Aircraft.N ASATM-87706,1986.4.Sprinkle,DannyR.; andShen, Chih-Ping:AMethod forMonitoringtheVariabilityinNuclear Absorption Charac-teristics ofAviationFuels.NASATM-4077,1988.5.Berger, M.J.; andHubbell,J.H.:XCOM: PhotonCrossSectionson a PersonalComputer.Rep.No. NBSIR-87/3597, National Bureau of Standards,July 1987.(Avai lable fromNTIS asPB88 109 830/HDM.)5

REPOR T DOCUMENTATIONPAGEForm ApprovedOMB No. 704-0188Publicreportingburdenforthiscollection of information is estimatedtoa verage1hourperresponse,includingthetimeforreviewing instructions,sear chingexistingdata sources,g atheringandmaintainingthe dataneeded,andcompletingandreviewingthe co llectionofinformation. Sendcomments regarding this burden estimateor anyother aspect of thisco llectionofinformatio n, including sugg estions forreducingthis burden,toWashingtonHeadquarter sServices,DirectorateforInformation OperationsandReports,1215JeffersonDav is Highway, Suite1204, Arlington,VA 22202-4302,andtotheOffice of ManagementandBudg et,Paperwork ReductionProject(0704-0188),Wa shingto n, DC20503.1 .AGENCYUSEONLY(Leaveblank)2.REPORT DATE3.REPORT TYPEAND DATESCOVEREDApril 1992TechnicalPaper4.TITLE ANDSUBTITLEFeasibility Study of a Low-EnergyGammaRaySystemforMeasuringQuantityandFlowRateofSlush Hydrogen6. AUT HOR(S)JagJ.Singh,Chih- Ping Shen, andDanny R.Sprinkle7. PERFORMINGORGANIZATION NAME(S) ANDADDRESS(ES)NASA LangleyResearchCenterHampton, VA23665-52259.SPONSO RING/ MONITORING AGENCYNAME (S)ANDAD DRESS(ES)National Aeronautics and SpaceAdministrationWashington, DC 20546-00015.FUNDINGNUMBERSWU307-50-10-028.PERFORMING ORGANIZATIONREPORTNUMBERL-1698010. SPONSORING/MONITORINGAGENCY REPORTNUMBERNASATP-315011. SUPPLEMENTARYNOTESSinghand Sprinkle:LangleyResearchCenter,Hampton,VA;Shen:OldDominionUniversity,Norfolk,VA.12a.DISTRIBUTION/AVAILABILITY STATEMENT1 2b. DISTRIBUTIONCODEUnclassied{UnlimitedSubjectCategory1913.ABSTRACT(Maxim um200words)Aspart of a studytodemonstr atethesuitability of anX-rayorgammarayprobeformonito ringthequantityandflow rateof slushhydrogen,mass attenuationcoefficientsforCd109X- and gammaradiation infivec hemicalcompoundshave beenmeasured.TheAg109KXrayswere usedforwaterandaceticacid,whereasE3 transitionfromthefirstexcitedstateat87.7keVinAg109providedtheprobe radiationforbromobenzene,ff2-chloroisodurene,a ndcetylbromide. Measurementswere madefor asinglephase(gas, liquid,andsolid)aswellasmixedphases(liquidplussolid)inall cases.It ha sbeen shownthat themass attenuationcoefficient forthe selected radiationsisindependentofthephase of thetestfluidsorphaseratios inthe case of mixed-phasefluid s.Thisreportdescribes theprocedureandresultsfor the ve uidsystemsinvestigated.14 . SUBJECTTERMS15. NUMBEROF PAGESSlush hydrogen; Multiphasechemicalsystems; Gamma rays;Massattenuationcoefficient;NationalAero-SpacePlane1 216. PRICECODEA0317. SECU RITYCLASSIFICATION18. SECURITYCLASSIFICATION19. SECURITYCLASSIFICATION20. LIMITATIONOF REPO RTOF THIS PAGEOF ABSTRACTOF ABSTRACTUnclassifiedUnclassifiedNSN 7540-01-280-5500Standard Form298(Rev. 2-89)Pre scr ibed byANSIStd. Z39-182 98 -102